Among the various closures made for the food and beverage industry is a "button" or "pop top" closure wherein the closure contains a flexible portion which assumes a given flexed position to indicate a sealed package and a different position when the package seal is breached. These "button" or "pop top" closures are commonly used in vacuum sealed food products such as baby food products to warn purchasers when the vacuum condition under which the food was packaged has been breached.
Although closures having tamper indicating buttons are predominantly in use in vacuum applications, there also have been more recently developed closures with buttons which are mechanically actuated so as to move from an as formed "down" position to an upwardly projecting "up" position when the closure is properly applied to a container. In this "up" position the closures are further characterized as having energy stored within the closure end panels urging the buttons to their as formed "down" position. Removal of these closures from the containers associated therewith results in the buttons moving to their as formed "down" position due to the release of the energy stored within the end panels.
Closures having end panels incorporating tamper indicating buttons are used extensively for the food industry, especially for vacuum packaged product, because they are effective quick-detection means that lets one know some very important conditions about the container. Typically in vacuum applications, when the container is properly sealed and a vacuum exists therein, the button is in a "down" position while when the container has been opened and the closure reapplied, or the vacuum within the container otherwise lost, the button will be in its "up" position. Additionally, in vacuum package applications, when the closure is first opened and the vacuum is lost, a hissing sound may be heard.
Through the extensive commercial use of such button closures, the purchasing public has become generally aware that if the deflectable section of the button is up then the original seal has been broken and that the container should be rejected. Additionally, in the case where the button closure is used in conjunction with a vacuum package container, the purchasing public has been sensitized to listen for a hiss of air or a "popping" sound to determine whether or not that container has been previously opened.
The popping of the top and, in the case of a vacuum packaged product, the sound associated with the loss of vacuum are indicating means to warn purchasers when the integrity of the package has been breached. These indicators, however, are not fool proof and can be intentionally overridden. For example, it is known that a button closure for a vacuum packaged product can be returned to its "tamper free" state even after the package has been opened. This is accomplished by merely heating the open container and when the container is hot, recapping the closure. This procedure will recreate the vacuum seal and reset the button.
Separate tamper evident means have been used in association with button caps to augment the flip or pop of the button. For example, button caps, and other screw top closures, are often used in association with a shrink wrap. Also, the button cap may be provided with a band at its base, joined to the remainder of the cap through a line of weakness. The band is prevented from rotating or from rising up the screw thread when the cap is unscrewed, and as a result, upon closure opening, the band becomes detached from the remainder of the cap.
The packaging industry has also recognized the desirability of providing a visual means to determine whether the integrity of a sealed container has been breached. For example, U.S. Pat. No. 3,736,899 (Manske) is directed to a pressure change indicator. The '899 patent discloses a button type cap having a flexible panel with a reflective surface and a disk-like element which covers up all or most of the flexible panel when the panel is flexed inward but which provides a gap around the periphery of the panel when it is flexed outward. The gap reveals a highly visible or contrasting color which is seen on the flexible panel either by means of a color on the panel itself or a color on the underside of the disk-like member. The pressure change system of the '899 patent apparently may be reestablished by recreating the vacuum in the package and, accordingly, in such a case would not be irreversible.
U.S. Pat. No. 4,429,803 (Butterfield) is directed to tamper evident means for multiple dose medical vials of the type having a rubber seal closure. The tamper evident means of the '803 patent is a blister-like sac containing a harmless dye. According to the '803 patent, the blister-like sac will release the dye and thereby color the remaining contents of the vial when the vial's seal is broken.
U.S. Pat. No. 4,511,052 (Klein et al.) is directed to a tamper indicating seal for a container. According to the '052 patent a frangible envelope containing an indicator is attached to the band and neck of the container having a closure so that when the closure is opened the frangible envelope will rupture and expose the indicator. The indicator can be a chemical substance which undergoes a change in color when exposed to the atmosphere such as an oxygen or moisture sensitive substance.
U.S. Pat. No. 4,526,752 (Perlman et al.) discloses a tamper evident package incorporating an oxygen sensitive leuco dye. According to the '752 patent, the oxygen sensitive leuco dye is sealed within the package in an anaerobic environment. The package can have a transparent cap through which the oxygen sensitive leuco dye is visible to show the integrity of the package. If oxygen is admitted to the package such as by opening the package, the dye will undergo a color change.
U.S. Pat. No. 4,813,712 (Scopes) is directed to providing a visible indication of whether a button cap is in its concave or convex form. According to the '712 patent the condition of the button can be determined by applying a pattern to the button surface which pattern can display one visible form when the surface is concave and a different visible form when the surface is convex. The different visible forms can include two different colors. In this regard, the '712 patent discloses a button cap having an embossed pattern wherein the pattern displays one color when in a given orientation such as concave and displays a different color when the orientation changes such as to convex. In another embodiment, the pattern is formed of superimposed layers which are displaced relative to one another when the surface changes between its concave and convex forms. Either the layers or the substrate for the layers contains a grid pattern which provides the closure with different appearances in the concave and convex forms. As noted in the '712 patent, a high degree of accuracy is required in laying down the patterns to ensure the colors register correctly with the embossed pattern to produce the desired visual result. Additionally, the surface indicating systems of the '712 patent appear to be reversible.
U.S. Pat. No. 4,877,143 (Travisano) is directed to a closure such as a button cap wherein the button carries an indicator such as a color or an imprinted word like "open" thereon. The indicator is covered with a translucent layer having a light diffusing surface which is provided by a Fresno lens. When the button is in the sealed position, the indicator is drawn away from the translucent/light diffusing layer which results in the indicator being obscured so that it cannot be seen through the translucent layer. When the container is opened and the button flips, the indicator is brought into contact with the translucent layer and the indicator becomes visible therethrough. Similar to the '712 (Scopes) patent above, the tamper evident system of the '143 patent appears to be a reversible system rather than an irreversible system.
Despite recognition of the need for tamper proof or tamper evident button closures, and responsive efforts related thereto there still exists the need for an improved tamper evident button closure.